Our long-term objective is to provide clinical and basic research and train at this Medical Center on the pathophysiology, diagnostic skill, and management of a variety of hemostatic and thrombotic disorders although our current proposal will focus on the microcirculation disorders such as thrombotic thrombocytopenic purpura (TTP), hemolytic uremic syndrome (HUS), progressive sclerosis, and multiple sclerosis. The specific aims of this proposal include: 1) purification and characterization of platelet aggregating factor in the TTP plasma and study of its interaction with platelets: 2) development of a sensitive immunoassay for TTP-PAF: 3) determination of the role of F VIII:vWF complex, PGI2, fibrinolytic activity and immune response in TTP; 4) study of the vivo effect of TTP plasma in animal models and therapeutic efficacy of various therapeutic agents; and 5) study of the effect of sera from patients with TTP, HUS, scleroderma, and multiple sclerosis on the endothelial cells, including cytotoxicity and fibrinolytic activity. The methods which will be used for the projects include conventional protein purification and characterization methods, immunoelectrophoresis, radioimmunoassay, platelet aggregation studies, fibrinolytic activity study, PGI2 bioassay and immunoassay, monoclonal antibody production, infusion of TTP plasma into mice, light and immunofluorescence microscopy, and electron microscopy.